1. Field of the Invention
This invention relates to a method for reactivation of spent inactive alumina-supported catalysts from a catalytic hydrotreating process. More particularly, this invention relates to method in which spent catalyst withdrawn from a hydrotreating process, such as H-Oil.RTM. hydrogenation process in which ebullated-bed reactors are employed, is first stripped of process oil by, for example, washing with a hydrocarbon solvent and the oil-free catalyst is then contacted with steam at an elevated temperature for a period of from about 2 to about 5 hours thereby providing a reactivated catalyst. In another aspect of this invention the reactivated catalyst is additionally regenerated by burnoff of the carbon and sulfur deposits under controlled conditions in the presence of an oxygen-containing gas or, if desired, the reactivated catalyst can be subjected to a rejuvenation step in which a part or substantially all of the metallic deposits are removed after which the rejuvenated catalyst can be regenerated by burnoff of the carbon and sulfur deposits.
During catalytic reaction processes, as exemplified by hydrotreating processes employing ebullated-bed reactors, the catalysts employed gradually are deactivated by virtue of an accumulation of carbonaceous deposits on the catalyst particles, and by virtue of various metallic elements such as vanadium, nickel, etc. being deposited thereon.
There is a need in the art for a practical method for conveniently reactivating spent hydrotreating catalyst withdrawn from a fluidized-bed catalytic reactor system, such as a processing system utilizing ebullated-bed or continuous stirred tank reactors in hydroprocessing high sulfur and metals-containing hydrocarbon feedstocks.
2. Prior Art
Canadian Patent No. 1,159,402 discloses a process for the recovery of used, contaminated catalyst according to particle density differences by fluidization in light liquid hydrocarbon fractions boiling in the range of 200.degree. to 450.degree. F., such as light naphtha, kerosene, fuel oil or water. This process is suitable for treating used catalyst derived from fluidized- or ebullated-bed reactors such as H-Oil.RTM. processes which involve continuous or periodic withdrawal of portions of used catalyst and their replacement with fresh catalyst thereby producing low-density and high-density fractions of used catalyst. The low-density fraction of the used catalyst may be regenerated by carbon burnoff after removal from the light hydrocarbon fluidization unit and before being returned to the reactor. The high-density fraction of used catalyst is, optionally, processed for recovery of deposited metals.
U.S. Pat. No. 3,809,644 discloses a process for multiple stage hydrodesulfurization of high sulfur, metals-containing petroleum residuum stocks in a multiple stage ebullated-bed hydrogenating process where catalyst used in the final stage reaction zone is removed and introduced without any additional treatment such as carbon burnoff, etc. to the preceding reaction zone thus extending the activity and effective life of the catalyst. In this process all fresh make-up hydrogen for the process is injected into the final reaction zone so that the hydrogen sulfide in the gas leaving that reaction zone is maintained below about three mole percent, thus substantially improving the desulfurization reaction rate in that reactor. The partially deactivated catalyst backstaged from the final stage reactor becomes guard-type contact solids for metals removal in the preceding stage reactor or reactors. Metals removal from the residual feedstocks can be maintained at the desired level without using high reaction temperatures. This process is reported to be especially effective when three reaction zones connected in series are employed and is applicable for producing low sulfur fuel oil from feedstocks containing 2 to 5 weight percent sulfur and having metals content ranging from about 20 p.p.m. vanadium to as much as 600 wppm (i.e., weight parts per million) vanadium.
U.S. Pat. No. 4,621,069 discloses a process for effective regeneration of used catalyst to remove deposited carbon and sulfur compounds by staged controlled burnoff and in this process the burnoff is accomplished by staged burnoff in multiple zones wherein the used particulate catalyst is introduced into a first zone where the catalyst is contacted at 300.degree.-500.degree. F. with an inert gas for 1-2 hours residence time to evaporate liquid components from the catalyst; the oil-free catalyst is then passed to a second zone wherein the catalyst in a thin bed is contacted at 780.degree.-800.degree. F. with a gas containing 0.5 to 1.0 V % oxygen in an inert gas for 4-6 hours residence time and finally, the partially regenerated catalyst is passed to a third zone where the catalyst in a thin bed is contacted with a gas containing 1-2 V % oxygen in an inert gas at a temperature of 800.degree.-850.degree. F. for 4-6 hours residence time and finally the further regenerated catalyst is passed to a fourth zone where the catalyst is contacted at 800.degree.-850.degree. F. with a gas containing 2-6 V % oxygen in an inert gas for 6-10 hours residence time to complete burnoff of carbon and sulfur deposits from the catalyst.
U.S. Pat. No. 4,720,473 discloses a process for treating a spent hydrotreating catalyst having an L/D greater than one by (1) stripping volatizable hydrocarbons to form free-flowing catalyst particles, (2) passing the free-flowing catalyst particles to a rotating drum length grading unit having indentations in the cylindrical wall where the catalyst particles with a length less than L.sub.1 are separated from the desired catalyst particles having a length greater than L.sub.1 the latter fraction comprising lightly contaminated particles and more heavily contaminated catalyst particles (Product A), (3) passing the Product A to a density grading unit utilizing gas suspension wherein the lightly metals contaminated catalyst particles are separated from Product A by contacting the suspended particles with an upwardly-sloping, vibrating surface. In a final step, the lightly metals contaminated catalyst particles having a length greater than L.sub.1 are passed to a regeneration zone in which carbonaceous deposits are removed in a controlled burnoff in the presence of an oxygen-containing inert gas at a temperature of about 200.degree. to 700.degree. C. Alternatively, the lightly contaminated catalyst particles from the density grading zone can be passed to a rejuvenation zone where the catalyst particles are acid leached to remove undesired metals from the catalyst particles which are then passed to a regeneration zone.
U.S. Pat. No. 4,454,240 discloses a catalyst regeneration process which includes a metal contaminants removal step. This procedure is particularly useful for recovering used catalyst from catalyst bed reaction systems such as H-Oil.RTM. and H-Coal.RTM. hydrogenation processes using ebullated-bed reactors, from fixed-bed catalytic reaction systems, and also from fluid catalytic cracking (FCC) processes. Preferred feedstocks for the reactor processes are from petroleum and coal. Catalyst having contaminant metals removed and regenerated by this process is said to have activity essentially equal to fresh catalyst. In the process of this patent the used catalyst is first washed with a hydrocarbon solvent such as naphtha, toluene, or mixtures thereof, etc. to remove process oils, the oil-free catalyst is then contacted for at least 5 minutes with an aqueous solution of sulfuric acid and an ammonium ion at a temperature of from 60.degree.-250.degree. F. which converts the metal contaminants to the respective soluble sulfate compounds. The metals-laden solution is drained off, after which the treated catalyst is washed with water to remove the residual aqueous solution and, in a final step, the washed, treated catalyst is subjected to a carbon burnoff in which the catalyst is contacted with a 1-6 V % oxygen in an inert gas mixture to remove carbon deposits.
U.S. Pat. No. 4,795,726 discloses a process for regenerating a spent alumina-based catalyst used in treating metal contaminated hydrocarbon feedstocks consisting essentially of an alumina support and containing one or more metals with hydrogenating activity in which the catalyst after being conventionally deoiled with toluene/pentane is contacted with steam at a temperature ranging from 390.degree.-930.degree. F. and then regenerated by carbon burnoff in the presence of an oxygen-containing gas. In a final step the regenerated catalyst is rejuvenated by treatment with a basic medium comprising a buffered aqueous solution of an ammonia or ammonium salt of a weak acid having a pH of 9-12 at a temperature of 5.degree.-100.degree. C.
U.S. Pat. No. 4,515,899 discloses a process for extending the useful life of vanadium-phosphorus-oxygen catalyst used in the production of maleic anhydride in fixed bed reactors in which the catalyst is regenerated by first contacting the catalyst with a phosphorus compound and finally contacting the catalyst with a flow of steam at a temperature of about 575.degree. F. to about 1110.degree. F.
British Patent Application 1526927 (October, 1978) discloses a process for the recovery of vanadium from a catalyst which has become inactivated in a process where a vanadium-containing hydrocarbon oil has been treated with hydrogen at elevated temperature and pressure. In this process the deactivated catalyst is treated with steam at a temperature above 390.degree. F. and in particular above 480.degree. F. for the purpose of removing at least a part of the sulfur and/or the coke present on the deactivated catalyst and then treated with an oxygen-containing gas prior to an acid extraction for the recovery of vanadium.